Substituent effect of a donor unit on electrochemical and opto-electronic properties of ambipolar benzotriazole-based polymers

Abstract

Two new donor–acceptor–donor (D–A–D) type monomers, 2-dodecyl-4,7-bis(4-methoxythiophen-2-yl)-2H-benzo[d] [1–3] triazole (MOTBT) and 2-dodecyl-4,7-bis(4-methylthiophen-2-yl)-2H-benzo[d] [1–3] triazole (MTBT) were synthesized by Stille coupling and the corresponding polymers, PMOTBT and PMTBT were obtained by electropolymerization method. The properties of the monomers and the polymers were studied by cyclic voltammetry (CV), ultraviolet–visible–near-infrared (UV–Vis–NIR) and spectroelectrochemistry. The CV results demonstrated ambipolar processes (n- and p-doping) for both polymers. According to the spectroelectrochemistry tests, the polymer PMOTBT revealed a saturated blue color in the reduced state and a transparent light blue color in the oxidized state, and the PMTBT polymer could switch between neutral orange color and oxidized light bluish-green color in the redox process. Furthermore, in the visible region, the optical contrasts were 51 % (at 645 nm) and 34 % (at 430 nm) for PMOTBT and PMTBT, respectively, with the switching times of 0.29 and 1.2 s from reduced state to oxidized state. In the NIR region, higher optical contrast ratios of 76 % (at 1600 nm for PMOTBT) and 67 % (at 1500 nm for PMTBT) as well as faster response times (0.90 and 0.35 s) were obtained. We also found that both polymers had the relative high coloration efficiency as much as 372 and 312 cm2/C and a satisfactory stability. Therefore, both polymers are promising candidates in displays and opto-electronic devices as electrochromic materials.